Quality of service aware handoff trigger

ABSTRACT

A method of estimating QoS for making a handoff trigger decision for a remote terminal in a wireless IP network is disclosed. At least a first and second probing packet is generated with an access router from a plurality of access points. The first and second probing packets are then sent from the access routers over a fixed core network having a plurality of routers to a correspondent access router and then back to the access routers. At least one collector packet is also generated and sent to follow the first and second probing packets to gather at least one predetermined QoS parameter from the routers after the first and second probing packets have left the routers. The QoS parameters are then processed with the access routers to make the handoff trigger decision preferentially along with layer two QoS parameters of the wireless hop.

FIELD OF THE INVENTION

[0001] The present invention relates generally to wireless communicationnetworks and more particularly to a quality of service aware handofftrigger for wireless communication devices.

BACKGROUND OF THE INVENTION

[0002] Quality of service (QoS) after handoff for networks with InternetProtocol (IP) based backbones has been receiving increased interest inthe networking research community. IP networks were originally notdesigned to provide QoS support and this handicap is even moresignificant for mobile networks. Real-time applications such as voiceover IP (VoIP) are particularly sensitive to QoS and have stringent QoSrequirements. Therefore, it is important to ensure adequate performanceon such metrics as latency, packet loss, packet jitter and that anadequate amount of bandwidth are provided after handoff.

[0003] Existing core network QoS probing tools can be divided into twocategories: passive and active probing techniques. Passive QoSestimation techniques generally consist of techniques that collect IPpackets on one or more links and record IP, TCP/UDP, orapplication-layer traces. These use existing traffic on the network anddo not inject additional probing packets into the network. The passivemonitoring approach has the advantage of not injecting additionalprobing traffic into the network. It observes the network as it is,meaning that the measurements are an assessment of true networkbehavior, since this latter is not disturbed by probing traffic intendedfor those measurements.

[0004] The monitoring can take different levels of granularity dependingon the degree of processing, storage and resources available. Packetmonitoring allows observation of packet-by-packet information such aspacket delay variation, packet size distribution, and throughput betweenhost pairs. Higher-level measurements, with less overhead, can beachieved by flow level measurements that record the total number ofbytes transferred, the flow start and finish time, among others.

[0005] As previously set forth, the main advantage of passive probingtechniques is that they do not introduce a load on the network theymonitor, which also means they do not distort the network traffic andtherefore produce realistic estimates. However their handicap is thatthey rely on existing traffic, which is not guaranteed to have desiredcharacteristics for certain measurements. For example, bottleneckbandwidth passive measurement techniques require a certain packet sizedistribution and inter-packet departure rate often not met, which is thecase for VoIP traffic. As it relates to the present invention, trafficis not guaranteed to exist through base station candidates at handofftime to the desired correspondent destination and as such relying onpassive monitoring is therefore inappropriate.

[0006] Active QoS estimation consist of techniques that actively injectmeasurement traffic into the network and compute metrics based on thereceived traffic at the receiver or the sender (round-trip or senderresponse). Active monitoring allows shaping the measurement traffic toapproximate user experience as much as possible. The disadvantage ofactive monitoring is that it sometimes adds a significant overhead tothe network in terms of traffic and processing, which may also lead to adistortion of the estimates of network behavior. Active monitoringtechniques can be generally categorized into two groups: InternetControl Message Protocol (ICMP) based and packet pair/train approaches.

[0007] The underlying concept used in the ICMP-based approach is that apacket sent with a time-to-live (TTL) equal to n will cause router n onthe path to identify itself since it will send back anICMP_time_exceeded message to the sender. A tool referred to as Pathcharis one of the earliest tools based on this technique. For each TTLnumber, Pathchar sends packets with varying sizes and observes theirone-way delay (half the observed round trip time). By successivelyincreasing the TTL, successive hops on the path are unraveled andrecursive subtractions of delays allow link-by-link QoS inference fordelay, packet loss, bandwidth and queue time.

[0008] The problem with Pathchar is the large amount of overhead itrequires. For example, 10 MB of data are required to measure a 10-hopEthernet path bandwidth. This approach is overkill for the purpose ofthe present invention since QoS estimation is required to occur throughseveral base stations for the handoff of each wireless terminal. Assuch, the Pathchar tool does not provide an optimal method of providinga QoS aware handoff trigger for VoIP applications.

[0009] As set forth above, the other active monitoring technique is thepacket-pair/train approach. Its main purpose is to obtain the bottleneckbandwidth, which is the link with the lowest transmission rate. Thisapproach consists of sending two packets or packet trains (severalpackets) through the path and inferring bottleneck bandwidth from packetinter-arrival times. In this approach the following underlyingassumptions are made: 1) the first packet does not experience queuing;and 2) following packets queue one after another at the bottleneck linkand at no other subsequent link.

[0010] If the assumptions are satisfied, packet inter-arrival times willbe proportional to the transmission rate of the bottleneck. Crosstraffic can cause the assumptions to be violated by causing undesirablequeuing or preventing probe packets from queuing after each other at thebottleneck. Filtering techniques have been proposed to work arounddistortions in measurements due to cross-traffic.

[0011] Voice applications will continue to be a major service ofinterest among wireless subscribers in future generation networks and assuch, a primary concern among wireless communication providers is todefine techniques capable of supporting QoS requirements upon handofftime. As such, a need exists for providing QoS to an IP-based corenetwork that assesses QoS performance through a fixed core network hop.In addition, a need exists for a method of combining the result withwireless hop signal power and signal-to-noise ratio (SNR) figures toassess the QoS on the end-to-end path.

SUMMARY OF THE PRESENT INVENTION

[0012] The present invention relates to a method of producing QoSestimates for the purpose of making a handoff trigger decision. The QoSestimates are used as the inputs to a base station selection algorithmas well as a load-balancing component that is added to that algorithm.The present invention also introduces optimization and tuning tocomplete the overall triggering mechanism. The decision to initiate ahandoff trigger relates to the QoS for the desired application perceivedthrough the current base station. The QoS estimation technique is usedon a regular basis to poll the current transmission path and rank itsperformance based on a QoS analysis. A result below a predefinedthreshold will initiate the trigger algorithm, which leads to probingthrough different base stations within radio range of the remoteterminal.

[0013] As briefly outlined above, a preferred embodiment of the presentinvention discloses a method of estimating QoS for making a handofftrigger decision for a remote terminal in a wireless IP network. In thepreferred embodiment, a first and second probing packet is generatedfrom each access router connected to an access point within radio rangeof the mobile terminal. The first and second probing packets are thensent from the access routers over a fixed core network having aplurality of routers to a correspondent access router and then back totheir originating access routers. A collector packet follows the firstand second probing packets to gather at least one predetermined QoSparameter from the routers after the first and second probing packetsleave the respective routers. The QoS parameters are then processed atthe access routers by algorithms in order to make the handoff triggerdecision. The access point providing the best QoS to the remote terminalfor its particular application will be designated to receive the handofffrom this estimation process.

[0014] The collector packets preferentially include a forward collectorpacket that is used to gather QoS parameters from the routers while thefirst and second probing packets are traveling across the fixed corenetwork from the access router to the correspondent access router. Thefirst and second probing packets are used to generate the QoS parametersthat are gathered by the collector packet. Preferentially, a reversecollector packet is used to gather the QoS parameters from the routerswhile the first and second probing packets travel back from thecorrespondent access router to the access router in which theyoriginated.

[0015] The forward and reverse collector packets are preferentially usedto record a packet queuing delay based on each probing packet at eachrouter, a packet transmission time based on each probing packet at eachrouter, a cumulated sum of queuing delays experienced by the first andsecond probing packets at each respective router, a transmission time ofthe first and second probing packets from the respective routers and acumulated sum of the current packet queuing delay experienced at therouters by the first and second probing packets.

[0016] In the preferred embodiment of the present invention, the QoSparameters that are collected are used to estimate one-way packet delayto form a basis for the handoff trigger decision. The QoS parametersthat are collected are also used to estimate the available bandwidth,which refers to the length of time from the moment the last bit of thepacket arrives at a link until its last bit leaves that link. Further,the QoS parameters are used to estimate packet jitter, which refers topacket inter-arrival times, to form a basis for the handoff triggerdecision.

[0017] In the preferred embodiment, at least one layer two QoS parametermay also be considered from the access point to the remote terminal whenmaking the handoff trigger decision. The layer two QoS parameters may beselected from a group of parameters consisting of bit error rate andsignal-to-noise ration. Further, each access point not having a signalstrength above an acceptable predetermined threshold can be removed fromconsideration when making the handoff trigger decision and thecorresponding fixed core hop from the corresponding access router to thedestination will not be subject to QoS estimation.

[0018] Although the present invention has been described as it relatesto making a handoff trigger decision in an all IP wireless network.Those skilled in the art should recognize that the present inventioncould also be used in network administration and monitoring as well. Assuch, the present invention should not be viewed as specifically limitedto QoS estimation in all IP wireless networks.

[0019] Further objects and advantages of the present invention will beapparent from the following description, reference being made to theaccompanying drawings wherein preferred embodiments of the invention areclearly illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 depicts an example of a preferred wireless IP network.

[0021]FIG. 2 depicts a packet transmission graph that illustrates intraand inter-flow queuing.

[0022]FIG. 3 depicts how inter-flows affect the flow of packets ofinterest through routers.

[0023]FIG. 4 illustrates parameters collected by a forward collectorpacket.

[0024]FIG. 5 illustrates the memory slot contents at each router.

[0025]FIG. 6 illustrates the information monitored by each router foreach probe group.

[0026]FIG. 7 illustrates parameters collected by the forward and reversecollector packets.

[0027]FIG. 8 illustrates the information that is provided by the firstand second probing packets.

[0028]FIG. 9 illustrates the QoS parameters combining rules.

[0029]FIG. 10 illustrates phase one and phase two of the QoS awarehandoff trigger.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS OF THEINVENTION

[0030] Referring to FIG. 1, a wireless IP network 10 is generallyillustrated that includes at least one remote terminal 12 and aplurality of correspondent nodes 14. The remote terminal 12 isillustrated as a voice enabled personal digital assistant (PDA) in FIG.1, but those skilled in the art would recognize that other remoteterminals such as wireless telephones may be used on the wireless IPnetwork 10. As such, the depiction of a voice enabled PDA in FIG. 1should be viewed in an illustrative sense and not as a limitation of thepresent invention. Further, the correspondent nodes 14 are illustratedin FIG. 1 as a fixed terminal and as a remote terminal to demonstratethe various types of communication devices that might be connected tothe wireless IP network 10.

[0031] As illustrated, the remote terminal 12 is connected to a basestation 16 that preferentially includes a radio tower 18, a server 20and an access router 22. The radio tower 18 is connected to the server20, which is in turn connected to the access router 22. Duringoperation, the radio tower 18 is used to conduct radio communicationbetween the remote terminal 12 and the server 20. The access routers 22are used to send and receive IP packets over the wireless IP network 10that contain voice data.

[0032] As further illustrated in FIG. 1, each access router 22 isconnected to at least one router 24, which are also used to transmitpackets over the wireless IP network 10. In reality, there is nofunctional difference between the access routers 22 and the routers 24however; the access routers 22 are designated separately in FIG. 1 toindicate their association with each particular base station 16. In thepreferred embodiment, each radio tower 18 and server 20 constitutes anaccess point that includes an access router 22, which can also bereferred to as an access point/access router pair. Those skilled in theart would recognize that when packets are transmitted over an IP networkthey can make several “hops” from router to router before arriving at arespective correspondent node 14. As used herein, a “hop” is a term ofart that is used to refer to packets traveling from one respectiverouter 22, 24 to another.

[0033] The wireless IP network 10 illustrated in FIG. 1 includes a corenetwork 26, which is used herein broadly to refer to the various networkcomponents that are used to interconnect access points to correspondentnodes 14. Those skilled in the art would recognize that severaldifferent network components could be used to interconnect the variouscomponents that make up the wireless IP network 10. Referring to FIG. 1,a public switch 28 can be connected to a private branch exchange 30 thatis connected to a respective correspondent node 14, which is illustratedas a fixed terminal. In this example, the correspondent node 14 which isset forth as a remote terminal 14, is connected to the core network 26via a fixed or wired hop 32. In the second example, the correspondentnode 14 is connected to the core network 26 through an access point,which represents a wireless hop 34.

[0034] Bandwidth is a term used to refer to the serialization speed adevice, such as remote terminal 12, is capable of obtaining on a networklink. The term bottleneck bandwidth is used to refer to the lowesttransmission capability among links on the entire path of the wirelessIP network 10. Estimating the bottleneck bandwidth, with respect to VoIPapplications, as well as others, is important because it can affect theQoS experienced by the remote terminal 12 during operation. For adetailed understanding of the present invention, it is important tounderstand how bottleneck bandwidth estimation techniques are used fornetworks.

[0035] Bottleneck bandwidth estimation techniques estimate the totalbandwidth of the bottleneck rather than the available bandwidth. Thedifference can be quite significant since total bandwidth refers to thecapacity each flow has when it has full control of the link whereas theavailable bandwidth will depend on the length of time from the momentthe last bit of the packet arrives at the link until its last bit leavesthat link. In the event of cross-traffic, that delay will includewaiting in the queue for other packets to be transmitted. With nocross-traffic, either from packets within the same flow (intra-flowqueuing) or packets from other flows (inter-flow queuing), totalbandwidth will be equal to available bandwidth.

[0036] Referring generally to FIG. 2, packets (k) and (k−1) belong tothe same flow. The delay, which is represented by(T_(l)^(k − 1) − t_(l)^(k))

[0037] is the inter-flow queuing time experienced by packet (k) at link(1), which means the waiting time of packet (k) for packets from otherflows to be transmitted. The equation (T_(l)^(k) − T_(l)^(k − l))

[0038] represents the intra-flow queuing time of packet (k) at link (1),meaning the waiting time of packet (k) for packet (k−1) to betransmitted from link (1). The total queuing time, which is (T₁ ^(k)−t₁^(k)), is the total queuing time of packet (k) at link (1) and isdenoted as q_(l) ^(k) in FIG. 2. As such, the available bandwidthexperienced by packet (k) at link (1) is represented as:

Baν_(l) ^(k) =s ^(k)/(s ^(k) /B _(l) +q _(l) ^(k))  (1)

[0039] In the absence of queuing time, the available bandwidth is equalto total bandwidth of the link.

[0040] The variable l in FIG. 2 is used to represent the last link onthe path the packet is traveling. The arrival time of packet (k) at link(1) is represented by t_(l) ^(k) and the queuing delay of packet (k) atlink (1) is represented by q_(l) ^(k). The propagation delay associatedwith link (1) is represented by d_(l). The transmission start time ofpacket (k) at link (1) is represented by T_(l) ^(k), wherein T_(l)^(k)=q_(l) ^(k)+t_(l) ^(k). The size in bits of packet k is representedby s^(k) and the total bandwidth of link (1) is represented by B_(l).The superscript in the equations represents the packet number and thesubscript is the hop number.

[0041] Any average has to be defined over a time scale and in thepresent invention the maximum resolution possible is used, meaning thetotal time needed for the transmission of one packet. Higher-level, butless accurate time scales could extend over several packets or an entireflow, but they will be less representative of actual performance asperceived by the user of the remote terminal 12. The present inventionmeasures the available bandwidth instead of the total bandwidth, sincethis is the throughput actually available to the application. It isimportant to note however that cross traffic from other flows andtraffic from the same flow as the application of interest will cause theavailable bandwidth to vary significantly over time.

[0042] The effect of inter-flow queuing is generally illustrated in FIG.3. As illustrated, it can be seen that the flow of the application ofinterest shares resources at intermediate routers 24 with other flowsthat are different at various hops. These interfering flows causepackets from the desired flow to queue and the queuing time lengthrelates to the arrival pattern and packet size distribution ofinterfering packet flows.

[0043] Another important factor the present invention is designed todeal with to improve QoS is one-way packet delay. One-way packet delayrefers to the latency in packet transmission from the time instant itsfirst bit leaves the sender until the last bit arrives at thedestination, which depends on several components broadly defined interms of processing time at the sender, the receiver and intermediatehops, transmission delay, propagation delay and queuing after otherpackets at each hop. The generalized one-way packet delay model isexpressed by the following equation: $\begin{matrix}{t_{l}^{k} = {A + t_{0}^{k} + {\sum\limits_{i = 0}^{l - 1}\left( {{s^{k}/B_{i}} + d_{i} + q_{i}^{k}} \right)}}} & (2)\end{matrix}$

[0044] Where A is a constant value identical for all packets of the samesize for the same application such as processing time at the sender,receiver and intermediate hops, framing and deframing of digitizedsignals for voice applications, etc. The queuing delay q_(i) ^(k) ofpacket (k) at link (i) is comprised of both inter-flow queuing time,meaning the waiting time of packet (k) for packets from other flows tobe transmitted and also intra-flow queuing time, meaning the waitingtime of packet (k) for packet (k−1) to be transmitted from link (i). SeeFIGS. 2 and 3.

[0045] Another factor affecting QoS is packet jitter, which representspacket inter-arrival time and is a random variable that is not average.Jitter can have two definitions:

[0046] 1) Jitter is equal to packet inter arrival time, as such it isthe random variable reflecting the variability in inter-arrival delay ofsuccessive packets from the same flow and as such is defined by:$\begin{matrix}{{\Delta \quad t_{l}^{k,{({k - 1})}}} = {{t_{l}^{k} - t_{l}^{k - 1}} = {{t_{0}^{k} - t_{0}^{k - 1} + {\sum\limits_{i = 0}^{l - 1}\left( {q_{i}^{k} - q_{i}^{k - 1}} \right)}} = {t_{0}^{k} - t_{0}^{k - 1} + {\sum\limits_{i = 0}^{l - 1}{\Delta \quad q_{i}^{k,{k - 1}}}}}}}} & \text{(3a)}\end{matrix}$

[0047]  Where Δ  q_(i)^(k, k − 1)

[0048]  is the difference in the queuing delays of packets (k) and (k−1)at hop (i).

[0049] 2) Jitter=Variance of packet latency (which is equivalent to thevariance of packet inter-arrival time) and is identified by:$\begin{matrix}{{\Delta \quad t_{l}^{k}} = \sqrt{{\sum\limits_{r = 1}^{k}{\left( t_{l}^{r} \right)^{2}/k}} - \left\lbrack {\left( {\sum\limits_{r = 1}^{k}t_{l}^{r}} \right)/k} \right\rbrack^{2}}} & \text{(3b)}\end{matrix}$

[0050]  Where Δt_(l) ^(k) is the k^(th) estimate of jitter at hop (1).Equations (3a) and (3b) assume packets (k) and (k−1) have same sizes^(k)=s^(k−1). It also assumes successive packets (k) and (k−1) followthe same path such that bandwidth B and propagation delay d is the sameat intermediate hops.

[0051] To estimate end-to-end QoS from the remote terminal 12 to thecorrespondent node 14, the present invention estimates QoS performanceby probing the fixed core network 26 and then combining the results withlayer 2 QoS measurements from the wireless hop, which is the hop fromthe base station 16 to the remote terminal 12. The results are combinedat each respective access router 22 that is associated with a particularbase station 16. A detailed description of how the present inventionprobes the fixed core network 26 for performance estimation is set forthin detail below.

[0052] As a first step to end-to-end QoS quantification, the presentinvention conducts probing from each candidate access router 22 to thecorrespondent node 14, regardless of whether the correspondent node 14is a fixed terminal (e.g.—telephone) or a wireless device. Since thepresent invention deals with making a handoff trigger decision, thoseskilled in the art should recognize that several candidate accesspoints, which have candidate access routers 22 associated with them,implement the probing step. If the correspondent node 14 is a wirelessdevice, the end-to-end QoS quantification takes place from access router22 to access router 22, respectively. In the case of a fixedcorrespondent node 14, probing will take place from access router 22that is connected to remote terminal 12 all the way to correspondentnode.

[0053] The essence of the preferred method disclosed by the presentinvention is that the only variable component in the link availablebandwidth (1), packet delay (2) and packet jitter (3) equations setforth above is the queuing delay experienced by packets. In equation(1), both packet size s^(k) and link bandwidth B_(l) are constant andidentical for all packets. The queuing delay q_(l) ^(k) is the onlyvariable element. Equation (2) indicates that the one-way delay of apacket has a constant component residing in (A+t₀ ^(k)). Also, packetsof the same size taking the same path will have an identical componentin$\sum\limits_{i = 0}^{l - 1}{\left( {{s^{k}/B_{i}} + d_{i}} \right).}$

[0054] . It follows that the only variable parameter is again queuingdelay. Finally, equation (3) includes a constant component equal to thedifference in packet departure times and again a variable component inqueuing time differences.

[0055] Active probing techniques all suffer from a basic limitation:they are only as good as the number of probes sent. Obviously,confidence in QoS estimates do not always increase linearly with thenumber of probes sent, but typically it is thought that a high number ofprobes are required to achieve as accurate a result as possible and makethe estimate significant for the desired use. In the past, the questionof how many probes to send has been difficult to answer in general andhave only been based on loose approximations of traffic patterns anddistributions.

[0056] The problem with the number of probes to use is two-fold. Undergeneral considerations, the higher the number of probes, the higher theburden on the wireless IP network 10. It is vital to avoid stressingnetwork resources, and even worse affecting the very traffic andperformance the present invention is trying to quantify. In addition,this end-to-end QoS estimation technique is done to determine handofftriggering and as such, there is a limited amount of time to perform theestimation since it has to take place during base station 16 coverageoverlap and possibly under fast user movement. It is estimated the timeavailable to make the handoff triggering decision will be betweenapproximately 1 to 3 seconds in future generation All-IP networks. Thepresent invention deals with all of the above-referenced issues by usingonly a few packets in the fastest way possible to make the handofftriggering decision.

[0057] A preferred embodiment of the present invention sends probingpackets through the core network 26, not with the intention of inferringQoS performance only by monitoring their transmission characteristics,but also by having the probing packets collect statistics alreadyavailable in the routers 24 on the end-to-end path. The QoS parameterequations as a function of queuing show that once the constant part ofthese expressions is known, only the queuing delay variation will beneeded to characterize performance. As set forth in greater detailbelow, the present invention uses two probing packets that are sent toquantify the invariable elements of the QoS parameter equations (1), (2)and (3). The variable queuing delay will be estimated at the routers 24and the results collected by forward and reverse collector packets.

[0058] Each respective router 24 in the preferred wireless IP network 10is required to maintain an updated estimate of the queuing time forpackets of different traffic categories, such as voice, video, or evenweb browsing, if required. Each packet is monitored for its queuing timein router buffers from arrival time of the last bit of the packet todeparture time of that last bit. Clock issues are not of relevance inthis case since time is measured as differences, all that is needed isfor the router clocks to run approximately at the same speed as the“true” clock. Each router 24 preferentially maintains a memory slot foreach traffic category that it updates with each new measurement ofpacket queuing time for the corresponding category.

[0059] For example, in the preferred embodiment of the present inventionthe update function used for voice at router (1) is represented as:$\begin{matrix}{{\hat{q}}_{l}^{voice} = {{a \times {\hat{q}}_{l_{old}}^{voice}} + {\left( {1 - \alpha} \right) \times q_{l}^{voice}}}} & (4)\end{matrix}$

[0060] Where: q̂_(l)^(voice)

[0061] is the new estimate to be stored by router (1) for voice packetqueuing times; q̂_(l_(old))^(voice)

[0062] is the previously stored estimate of voice packet queuing time atrouter (1); q_(l)^(voice)

[0063] is the last observed queuing time for a voice packet at router(1); and α is the tuning factor such that a larger α value gives moreweight to the old estimate, leading to slower sensibility to fastvariations. Smaller α values yield faster response to queuing timevariations but also less stability in the estimate.

[0064] Each router 24 is also required to keep track of inter-packetarrival time for packets from the same traffic category. This requirestwo memory slots per traffic category. When voice is considered, onememory slot will be used for the previously observed queuing timeq_(l_(previous))^(voice)

[0065] of a voice packet at router (1) and another for the estimatedjitter contribution Δ̂  q_(l)^(voice)

[0066] introduced by router (1) for voice packets.

[0067] As set forth in the following equation, the estimated jitter atthe router 24 is updated similarly to the queuing delay estimate inequation (4): $\begin{matrix}{{\hat{\Delta}\quad q_{l}^{voice}} = {{a \times \hat{\Delta}\quad q_{l_{old}}^{voice}} + {\left( {1 - \alpha} \right) \times \left( {q_{1}^{voice} - q_{l_{previous}}^{voice}} \right)}}} & (5)\end{matrix}$

[0068] Where: {circumflex over (Δ)}q_(l) ^(voice) is the new estimate tobe stored by router (1) for voice packet jitter contribution at thatrouter; Δ̂  q_(l_(old))^(voice)

[0069] is the previously stored estimate of voice packet jittercontribution at router (1); q_(l) ^(voice) is the last observed queuingtime for a voice packet at router (1); and   q_(l_(previous))^(voice)

[0070] is the previously stored queuing time for a voice packet atrouter (1).

[0071] Upon triggering of the QoS estimation functionality, eachrespective access router 22 that is a candidate for the handoff of theremote terminal 12 will send three (3) probes to the correspondent node14. In the preferred embodiment, the first two probes will be packetshaving the size and characteristics of voice packets and the thirdpacket will be intended as a collector of information. The three packetsare to be identified as a probe group through a common ID. The accessrouter 22 is required to monitor the round-trip delay of the first twoprobes. Since the first two probes have identical characteristics tovoice traffic in terms of size, interdeparture rate at the sender, andQoS class if any, they will be subject to transmission conditionsidentical to those of voice at intermediate hops in the fixed corenetwork 26.

[0072] When the first voice-like probe packet reaches the access routerof the correspondent node 14, the access router sends back a similarpacket to the originating access router 22 after recording arrival anddeparture times. The same happens for the second voice-like probepacket. When the second probe is transmitted back, a reverse collectorpacket will be sent to the access router 22 for the same purposes as theforward collector packet. In addition, the forward collector packet issent back to the access router 22 to provide it with the collectedforward path information.

[0073] Each router 24 is required to monitor the queuing timeq_(l)^(probe₁)

[0074] and q_(l)^(probe₂)

[0075] of the first two probing packets, and store them in memory.Preferentially, the queuing time estimate of the corresponding trafficcategory is not updated based on the probe queuing times since thesetimes do not really reflect authentic traffic behavior. In addition,each router 24 has to monitor the transmission time (s^(probe) ^(₁)/B_(l)) and (s^(probe) ^(₂) /B_(l)) of probe packets 1 and 2respectively from their link. Those values will be stored until thecollector packet belonging to that probe group arrives at the router 24.Timeout functionalities will also be introduced to delete the monitoredresults in case the collector packet is lost and never arrives tocollect that information.

[0076] The collector packet coming from the source, i.e. access router22, also referred to herein as the forward collector packet, since it ison the forward path towards the destination, will traverse routers 24traversed by the previous two probe packets and collect the informationset forth in FIG. 4 on probes 1 and 2 and the routers 24. Field 1 inFIG. 4 represents the cumulated sum of queuing delays recorded by therouters 24 for probe 1. Field 2 is the maximum observed delay from lastpacket bit arrival to last packet bit departure at intermediate routers24 for probe 1. Field 3 and 4 in FIG. 4 are identical to 1 and 2respectively except that they relate to probe 2. Field 5 is thecumulated sum of estimated queuing delays for this traffic category bythe routers 24 along the path for packets of this traffic category.Field 6 is the cumulated sum of estimated packet jitter contributions byrouters 24 along the path for packets of this traffic category.

[0077] The need for a collector packet comes from the impossibility ofrecording timing of packet transmission times within the packet itselfsince it would have departed. In addition, the recording process intothe packet can distort the delay estimate since it introduces additionallatencies. Since the categories of relevance in terms of QoSrequirements are limited, this approach scales well both in terms ofprocessing and memory space requirements at each router 24.

[0078] In order to keep track of the necessary information that theforward and reverse collector packets require, memory slots are used ateach router 24. FIG. 5 illustrates the memory slots used and thecontents of each memory slot. As set forth in FIG. 5, each router 24 hasto keep track of each packet's queuing time. It also has to performsimple calculations of subtraction, multiplication and addition andupdate three memory slots for each packet it transmits. As furtherillustrated in FIG. 6, for each probe group each router 24 also has tomonitor probe queuing delay and transmission delay.

[0079] After the forward and reverse collector packets have returned,the information they contain must be processed by the correspondingaccess router 22. As such, the information processing to estimate QoSover the core network 26 hop is performed at each respective candidateaccess router 24. After receiving the forward and reverse collectorpackets, each respective access router 22 will have the data illustratedin the table set forth in FIG. 7. As a result, the first and secondprobes received back at each access router 22 provide the data set forthin the table illustrated in FIG. 8.

[0080] The previous discussion on equation (2) showed that one-way delaycan be rewritten in terms of a fixed component common to all packets:$C_{Fix} = {A + t_{0}^{k} + {\sum\limits_{i = 0}^{l - 1}\left( {{s^{k}/B_{i}} + d_{i}} \right)}}$

[0081] and a variable component$C_{Var} = {\sum\limits_{i = 0}^{l - 1}{q_{i}^{k}.}}$

[0082] . C_(Fix) only needs to be calculated once and we propose toinfer it from delay measurements on probes 1 and 2. A correct estimateof C_(var) combined with the value of C_(Fix) will provide a goodestimate for one-way delay. For voice applications, if$\sum\limits_{i = 0}^{l - 1}q_{i}^{probe}$

[0083] is subtracted from the measured one-way delay and$\sum\limits_{i = 0}^{l - 1}{\hat{q}}_{i}^{voice}$

[0084] is added, it effectively adjusts the measure of one-way delay bya more accurate estimation of the variable component C_(var).

[0085] If the clocks at the access routers 22 and correspondent node 14are not synchronized, we will have to rely on measured RTT at the accessrouter 22 and divide by two. Equation (6) below is an expression for theestimated one-way delay using the values described in the tables setforth in FIGS. 7 and 8. $\begin{matrix}{\hat{\tau} = {{{1/4} \times {\sum\limits_{j = 1}^{2}\left\{ {{RTT}_{{probe}_{j}} - \left( {\sum\limits_{i = 0}^{l - 1}q^{{probe}_{j}}} \right)_{forward} - \left( {\sum\limits_{i = 0}^{l - 1}q^{{probe}_{j}}} \right)_{reverse}} \right\}}} + {{1/2} \times \left\{ {\left( {\sum\limits_{i = 0}^{l - 1}{\hat{q_{i}}}^{voice}} \right)_{forward} + \left( {\sum\limits_{i = 0}^{l - 1}{\hat{q_{i}}}^{voice}} \right)_{reverse}} \right\}}}} & (6)\end{matrix}$

[0086] The above-referenced expression uses an averaging of the delaysinferred from probes 1 and 2 respectively.

[0087] The disadvantage with using the RTT is that there is noconsideration for asymmetric links that are often encountered inpractical networks. Synchronized clocks at the access router 22 and thecorrespondent node 14 will provide a better way to address that problem.In that case, two values of delay can be defined, one for the forwardand one for the reverse path, by once again using the values describedin the tables set forth in FIGS. 7 and 8 as follows: $\begin{matrix}{{\hat{\tau}}_{forward} = {{{1/2} \times {\sum\limits_{j = 1}^{2}\left\{ {\left( {t_{CN}^{{probe}_{j}} - T_{AR}^{{probe}_{j}}} \right) - \left( {\sum\limits_{i = 0}^{l - 1}q^{{probe}_{j}}} \right)_{forward}} \right\}}} + \left( {\sum\limits_{i = 0}^{l - 1}{\hat{q}}_{i}^{voice}} \right)_{forward}}} & (7) \\{{\hat{\tau}}_{reverse} = {{{1/2} \times {\sum\limits_{j = 1}^{2}\left\{ {\left( {t_{AR}^{{probe}_{j}} - T_{CN}^{{probe}_{j}}} \right) - \left( {\sum\limits_{i = 0}^{l - 1}q^{{probe}_{j}}} \right)_{reverse}} \right\}}} + \left( {\sum\limits_{i = 0}^{l - 1}{\hat{q}}_{i}^{voice}} \right)_{reverse}}} & (8)\end{matrix}$

[0088] In another preferred embodiment of the present invention thefollowing equation can be used to estimate the one-way packet delay onthe forward and reverse path:$\tau_{n}^{\hat{k}} = {\left\lbrack {{1/2} \times {\sum\limits_{j = 1}^{2}\left( {t_{Dest}^{{probe}_{j}^{k}} - {\underset{l = 0}{\overset{n - 1}{T_{Src}^{{probe}_{j}^{k}} - \sum}}q_{l}^{{probe}_{j}^{k}}}} \right)}} \right\rbrack + \left( {\sum\limits_{l = 0}^{n - 1}{\hat{q}}_{l}^{k,{voice}}} \right)}$

[0089] The next item that needs to be estimated is jitter. As set forthabove, equation (3) is used for estimating jitter delay at the routers24 and is given by the following equations:

[0090] First definition of jitter:${\Delta \quad t_{l}^{k,{({k - 1})}}} = {t_{0}^{k} - t_{0}^{k - 1} + {\sum\limits_{i = 0}^{l - 1}{\Delta \quad {q_{i}^{k,{k - 1}}.}}}}$

[0091] Second definition of jitter:${\Delta \quad t_{l}^{k}} = \sqrt{{\sum\limits_{r = 1}^{k}{\left( t_{l}^{r} \right)^{2}/k}} - \left\lbrack {\left( {\sum\limits_{r = 1}^{k}t_{l}^{r}} \right)/k} \right\rbrack^{2}}$

[0092] Based on this equation, the following two equations for forwardand reverse jitters are used in one embodiment (corresponding to thefirst definition of jitter): $\begin{matrix}{{\Delta \quad t_{l\quad {forward}}^{k,{({k - 1})}}} = {T_{AR}^{{probe}_{2}} - T_{AR}^{{probe}_{1}} + {\sum\limits_{i = 0}^{l - 1}{\hat{\Delta}\quad q_{i\quad {forward}}^{voice}}}}} & (9) \\{{\Delta \quad t_{l\quad {reverse}}^{k,{({k - 1})}}} = {T_{CN}^{{probe}_{2}} - T_{CN}^{{probe}_{1}} + {\sum\limits_{i = 0}^{l - 1}{\hat{\Delta}\quad q_{i\quad {reverse}}^{voice}}}}} & (10)\end{matrix}$

[0093] In another preferred embodiment of the present invention(corresponding to the second definition of jitter) the followingequation can be used for forward and reverse jitter estimates:${\Delta \quad t_{n}^{k}} = \sqrt{{\left( \tau_{n}^{\hat{k}} \right)^{2}/k} + {\left( {1/k} \right) \times {\sum\limits_{r = 1}^{k - 1}\left( \tau_{n}^{\hat{r}} \right)^{2}}} - {\left( {1/k^{2}} \right) \times \left\lbrack {{\sum\limits_{r = 1}^{k - 1}\tau_{n}^{\hat{r}}} + \tau_{n}^{\hat{k}}} \right\rbrack^{2}}}$

[0094] The next item that needs to be estimated is the minimum availablebandwidth. The minimum available bandwidth corresponds to the maximumdelay encountered at a router 24 since this delay can be due to either aqueuing bottleneck or bandwidth bottleneck, therefore reflectingavailable bandwidth. The minimum available bandwidth is the only valueneeded to characterize the path bandwidth since path bandwidth is onlyas good as the worst link. The expressions of available bandwidth usingvalues from the tables set forth in FIGS. 7 and 8 are: $\begin{matrix}{{Bav}_{forward} = {{1/2} \times {\sum\limits_{j = 1}^{2}{{s^{{probe}_{j}}/{Max}}\left\{ {{\left( {q_{i}^{{probe}_{j}} + {s^{{probe}_{j}}/B_{i}}} \right);{i = 0}},\ldots \quad,\left( {l - 1} \right)} \right\}_{forward}}}}} & (11) \\{{Bav}_{reverse} = {{1/2} \times {\sum\limits_{j = 1}^{2}{{s^{{probe}_{j}}/{Max}}\left\{ {{\left( {q_{i}^{{probe}_{j}} + {s^{{probe}_{j}}/B_{i}}} \right);{i = 0}},\ldots \quad,\left( {l - 1} \right)} \right\}_{reverse}}}}} & (12)\end{matrix}$

[0095] Notice that the above expression averages the available bandwidthestimated by probes 1 and 2 respectively.

[0096] In another preferred embodiment of the present invention, thefollowing equation can be used to estimate the available bandwidth onthe forward and reverse paths:${Bav}^{k} = {{1/2} \times {\sum\limits_{j = 1}^{2}{{s^{{probe}_{j}^{k}}/{Max}}\left\{ {{\left( {{\hat{q}}_{l,{probe}_{j}^{k + s^{{probe}_{j}^{k}}}}^{voice}/B_{l}} \right);{l = 0}},\ldots \quad,\left( {n - 1} \right)} \right\}}}}$

[0097] Another preferred embodiment of the present invention is directedtoward optimizing the QoS estimation technique by avoiding redundantmeasurements. The handoff triggering mechanism of each remote terminal12 will cause QoS estimation through several access routers 22 andcorresponding paths of the core network 26 to the same correspondentnode 14. One optimization will be to identify common portions on thesedifferent paths of the core network 26 and avoid collecting theirqueuing information twice.

[0098] Another optimization technique that may be used in the presentinvention is to eliminate wireless hops 34 with bad signals with respectto the remote terminal 12 as candidates for handoff. Again, theend-to-end QoS estimation will include both layer 2 information and corenetwork layer 3 QoS evaluation. However, since the path is only as goodas its weakest link another optimization will be not to perform probingon the fixed core network 26 portion if the corresponding wireless hop34 has a very bad signal, as compared to a threshold value.

[0099] Another optimization that is envisioned by the present inventionrelates to the monitoring that is conducted at the routers 24. Thepreferred embodiment of the present invention also can optimize therouter 24 monitoring functionality of regular traffic from differentcategories. Instead of monitoring each packet for its queuing time andupdating the queuing time estimate, the routers 24 can be set up toconduct monitoring at separated intervals, either regular or random. Assuch not every packet is monitored, a subset only is tracked and queuingtime estimate adjustment is achieved based on this subset only. Thiswill have the advantage of reducing the load on the router 24 resources.

[0100] As used herein, layer 2 measurements refer to parameters over thewireless hop 34, which preferentially include Bit Error Rate (BER),Frame Error Rate (FER), Signal-to-Noise Ratio (SNR),Carrier-to-Interference ratio (C/I), received wireless signal power,throughput in bits/sec (average, peak, minimum), goodput in bits/sec(average, peak, minimum). Goodput refers to throughput measurement ofall payload bits transmitted, excluding headers), frame loss ratio,frame latency, and frame latency variation. Frame refers to the groupsof bits at layer 2, the same as a packet at layer 3. The QoS estimationtechnique required for QoS-aware triggering has to be end-to-end andtherefore has to extend from the remote terminal 12 all the way to thecorrespondent node 14. As illustrated in FIG. 1, the correspondent node14 can either be fixed or mobile.

[0101] In the case of a fixed correspondent node 14, QoS estimationthrough the fixed core network 26 has to extend from the access router22 connected to the remote terminal 12 to the correspondent node 14. Theaccess router 22 collects QoS data about the fixed core network 26, QoSdata about the wireless hop 34 from the access point to the remoteterminal 12 and QoS data about the fixed hop 32 to the correspondentnode 14. The access router 22 is responsible for combining these figuresand producing an end-to-end QoS estimate about the path.

[0102] The layer 3 fixed core network 26 QoS parameters and the layer 2wireless hop 34 QoS parameters are combined as follows: a thresholdT_(layer2) is set for signal power or SNR on the wireless hop 34. AQoS_Ranking figure is obtained for the fixed core network 26, which isobtained as generally set forth below. Collected layer 2 QoS data havefirst to comply with threshold T_(layer2). Only then is selectionperformed on the QoS_Ranking value of the hop over the fixed corenetwork 26. Another approach can be to map layer 2 QoS parameters of thewireless hop 34 into layer 3 QoS parameters and combine the wireless hop34 and fixed hop layer 3 QoS before obtaining the QoS_Ranking value forthe path. Once it is obtained, path selection will be solely based onthe QoS₁₃ Ranking parameters.

[0103] Rules for combining delay, jitter, bandwidth and packet loss aredefined as set forth below and FIG. 9. For wireless correspondent nodes14, the measurement is performed between the access routers 22 that areconnected to the remote terminal 12 and the correspondent nodes 14 andwireless link layer 2 QoS has to be collected on two wireless hops 34,the remote terminal 12 to its access point hop and the correspondentnode 14 to its access point hop.

[0104] As illustrated in FIG. 10, the discussion above defined the QoSestimation algorithm and how it is used in the preferred embodiment ofthe present invention. This is referred to as phase one of the QoS-awarehandoff trigger, which is generally illustrated in FIG. 10. Phase two,which is the next step, is access router 22 and access point selectionbased on the end-to-end QoS parameter estimates.

[0105] In phase two, an access router 22, at a particular access point,is selected based on a QoS_Ranking parameter that is obtained usingeither a weighting based ranking or a perception based ranking. Once theQoS_Ranking parameter is obtained each access router 22 at each accesspoint is classified or ranked in the order of providing the best QoS tothe remote terminal 12. As further illustrated in FIG. 10, then loadbalancing is taken into consideration and finally, cost awareness anduser preferences may also be taken into consideration when making thehandoff trigger decision. Ultimately a handoff trigger decision is madebased on all of the considerations outlined herein.

[0106] As generally set forth above, in the preferred embodiment of thepresent invention, the selection algorithm will preferentially alsoinclude a load balancing functionality. The reason is to avoid anunusually higher performance base station 16 to be overwhelmed byhandoffs, especially under the case of several remote terminals 12within the same radio coverage area using the same fixed core network26. The load balancing function is based on a randomizer, such thatgiven a set of n access points with acceptable QoS and corresponding nQoS_Ranking values, then select access points (i) with probability:$\begin{matrix}{\left( {QoS\_ Ranking}_{i} \right)/{\sum\limits_{j = 1}^{n}\quad {QoS\_ Ranking}_{j}}} & (5)\end{matrix}$

[0107] The preferred handoff triggering method is application specific,meaning that the trigger takes into consideration the requirements of aspecific application and attempts to satisfy it by proper triggering.All the methods described assume the existence of a correspondent node14 to which traffic is to be directed after handoff and QoS measurementswill be directed towards that correspondent node 14.

[0108] The rationale is that different applications have different QoSrequirements and it is not trivial to find a common set of requirementssatisfying all applications at the same time and that we can input intothe handoff triggering algorithm. The preferred embodiment of thepresent invention focuses on limiting the scope of requirements to voicealone, especially since such a service will be a minimum objective forfuture generation mobile networks. Future work will aim at identifying amethodology for grouping different application QoS requirements into oneset over which to base the trigger.

[0109] The case may occur that no voice call is ongoing at handoff time.The correspondent node 14 is therefore unidentified. This scenario isleft out from the scope of the present report. However a simpletemporary solution is to switch back to regular layer 2 QoS measurementsover the wireless link 34 much like the current wireless networks.

[0110] Referring to FIG. 10, phase two of the present inventiondiscloses a method for providing a triggering mechanism in an IPwireless communication system 10. This method includes the steps ofprobing a plurality of communication paths between a mobile terminal anda correspondent node to obtain at least one QoS parameter associatedwith each said communication path; identifying each communication paththat provides a predetermined acceptable level of performance; andgenerating a handoff trigger to the communication path that provides thehighest level of performance to the remote terminal 12.

[0111] Yet another preferred embodiment of phase two discloses a methodand system for providing a triggering mechanism for a mobile terminal inan all-IP wireless communication system. The preferred method comprisesthe steps of: probing a plurality of access points with the remoteterminal 12 to obtain at least one QoS parameter that is defined by acommunication traffic path between the remote terminal 12 and acorrespondent node 14; classifying each access point into a group thatpasses a predefined QoS requirement associated with the QoS parameter;ranking the group according to a predicted level of performance byquantifying the QoS parameter; and generating a handoff triggerdirecting the remote terminal 12 to hand off to the access pointproviding the highest QoS to the remote terminal 12.

[0112] In the preferred embodiment, the at least one QoS parameter isselected from a group of layer 3 QoS parameters consisting of packetdelay, packet jitter, packet loss and bandwidth on an end-to-end path.In addition, in one embodiment the first group is ranked using aweighted-based ranking. In yet another embodiment, the first group isranked using a perception-based ranking.

[0113] For a detailed discussion of phase two, which involves the accessrouter 22 and access point selection, please refer to co-pending U.S.application Ser. No.: 09/965,437 entitled Layer Three Quality of ServiceAware Trigger, which is incorporated herein by reference in itsentirety.

[0114] While the invention has been described in its currentlybest-known modes of operation and embodiments, other modes, embodimentsand advantages of the present invention will be apparent to thoseskilled in the art and are contemplated herein.

What is claimed is:
 1. A method of estimating QoS in an IP network,comprising the steps of: generating at least a first and second probingpacket with an access router from at least one access point; sendingsaid first and second probing packets from said at least one accesspoint over a fixed core network having a plurality of routers to acorrespondent access router and then back to said at least one accessrouter; sending at least one collector packet to follow said first andsecond probing packets to gather at least one predetermined QoSparameter from said routers after said first and second probing packetsleave said routers; and processing said at least one QoS parameter withsaid at least one access router to determine a level of QoS experiencedby said at least one access router.
 2. The method of claim 1, whereinsaid at least one collector packet comprises a forward collector packetfor gathering said at least one QoS parameter from said routers whilesaid first and second probing packets are traveling from said at leastone access router to said correspondent access router.
 3. The method ofclaim 1, wherein said at least one collector packet comprises a reversecollector packet for gathering said at least one QoS parameter from saidrouters while said first and second probing packets are traveling fromsaid correspondent access router to said at least one access router. 4.The method of claim 1, further comprising the step of recording a packetqueuing delay based on each said probing packet at each said router. 5.The method of claim 1, further comprising the step of recording a packettransmission time based on each said probing packet at each said router.6. The method of claim 1, wherein said at least one QoS parametercomprises a cumulated sum of queuing delays experienced by said firstand second probing packets at each respective router.
 7. The method ofclaim 1, wherein said at least one QoS parameter comprises atransmission time of said first and second probing packets from saidrespective routers.
 8. The method of claim 1, wherein said at least oneQoS parameter comprise a cumulated sum of the current packet queuingdelay experienced at said routers by said first and second probingpackets.
 9. The method of claim 1, wherein said first and second probingpackets are formed having similar characteristics as voice trafficpackets.
 10. The method of claim 1, wherein said at least one QoSparameter is used to estimate one-way packet delay.
 11. The method ofclaim 1, wherein said at least one QoS parameter is used to estimateavailable bandwidth.
 12. The method of claim 1, wherein said at leastone QoS parameter is used to estimate packet jitter.
 13. The method ofclaim 1, further comprising the step of avoiding the gathering of saidat least one QoS parameters by said collector packets for each routeralready visited by a first and second probing packet from another accessrouter.
 14. A method of estimating QoS in an IP network, comprising thesteps of: sending a first and second probing packet across a fixed corenetwork from a plurality of candidate access routers to a correspondentaccess router; sending a forward collector packet that follows saidfirst and second probing packet across said fixed core network to saidcorrespondent access router, wherein said forward collector packetcollects a predetermined set of parameters from said routers; sendingsaid first and second probing packet and said forward collector packetback to said originating access router from said correspondent accessrouter; sending a reverse collector packet that follows said first andsecond probing packet across said fixed core network to said originatingaccess router from said correspondent access router, wherein saidreverse collector packet collects a second predetermined set ofparameters from said routers; and processing the first and secondpredetermined set of parameters from said forward and reverse collectorpackets to determine a level of QoS experienced by said candidate accessrouter.
 15. The method of claim 14, further comprising the step ofrecording a packet queuing delay at each said router.
 16. The method ofclaim 14, further comprising the step of recording a packet transmissiontime at each said router.
 17. The method of claim 14, wherein said firstand second predetermined set of parameters include a cumulated sum ofqueuing delays experienced by said first and second probing packets ateach said respective router.
 18. The method of claim 14, wherein saidfirst and second predetermined set of parameters include a transmissiontime of said first and second probing packets from each said respectiverouter.
 19. The method of claim 14, wherein said first and secondpredetermined set of parameters include a cumulated sum of the currentpacket queuing delay at said routers.
 20. The method of claim 14,wherein said first and second probing packets are formed with the samecharacteristics as voice traffic packets.
 21. The method of claim 14,wherein said first and second predetermined set of parameters are usedto estimate one-way packet delay.
 22. The method of claim 14, whereinsaid first and second predetermined set of parameters are used toestimate available bandwidth.
 23. The method of claim 14, wherein saidfirst and second predetermined set of parameters are used to estimatepacket jitter.
 24. The method of claim 14, further comprising the stepof avoiding the gathering of said first predetermined set of parametersfor routers already visited by a first and second probing packet fromanother access router.
 25. The method of claim 14, further comprisingthe step of avoiding the gathering of said second predetermined set ofparameters for routers already visited by a first and second probingpacket from another access router.
 26. A method of estimating QoS formaking a handoff trigger decision for a remote terminal in a wireless IPnetwork, comprising the steps of: generating at least a first and secondprobing packet with an access router from a plurality of access points;sending said first and second probing packets from said access pointsover a fixed core network having a plurality of routers to acorrespondent access router and then back to said access routers;sending at least one collector packet to follow said first and secondprobing packets to gather at least one predetermined QoS parameter fromsaid routers after said first and second probing packets leave saidrouters; and processing said at least one QoS parameter with said accessrouters to make said handoff trigger decision.
 27. The method of claim26, further comprising the step of considering at least one layer twoQoS parameter from said access point to said remote terminal when makingsaid handoff trigger decision.
 28. The method of claim 27, wherein eachsaid access point not having a signal strength for a wireless hop abovean acceptable predetermined threshold is removed from consideration whenmaking said handoff trigger decision.
 29. The method of claim 27,wherein said layer two QoS parameters may be selected from a group ofparameters consisting of Bit Error Rate (BER), Frame Error Rate(FER),-Signal-to-Noise Ratio (SNR), Carrier-to-Interference ratio (C/I),received wireless signal power, throughput in bits/sec (average, peak,minimum), goodput in bits/sec (average, peak, minimum), frame lossratio, frame latency, and frame latency variation.
 30. The method ofclaim 26, wherein said at least one collector packet comprises a forwardcollector packet for gathering said at least one QoS parameter from saidrouters while said first and second probing packets are traveling fromsaid access router to said correspondent access router.
 31. The methodof claim 26, wherein said at least one collector packet comprises areverse collector packet for gathering said at least one QoS parameterfrom said routers while said first and second probing packets aretraveling from said correspondent access router to said access router.32. The method of claim 26, further comprising the step of recording apacket queuing delay based on each said probing packet at each saidrouter.
 33. The method of claim 26, further comprising the step ofrecording a packet transmission time based on each said probing packetat each said router.
 34. The method of claim 26, wherein said at leastone QoS parameter comprises a cumulated sum of queuing delaysexperienced by said first and second probing packets at each respectiverouter.
 35. The method of claim 26, wherein said at least one QoSparameter comprises a transmission time of said first and second probingpackets from said respective routers.
 36. The method of claim 26,wherein said at least one QoS parameter comprise a cumulated sum of thecurrent packet queuing delay experienced at said routers by said firstand second probing packets.
 37. The method of claim 26, wherein saidfirst and second probing packets are formed having similarcharacteristics as voice traffic packets.
 38. The method of claim 26,wherein said at least one QoS parameter is used to estimate one-waypacket delay to form a basis for said handoff trigger decision.
 39. Themethod of claim 26, wherein said at least one QoS parameter is used toestimate available bandwidth to form a basis for said handoff triggerdecision.
 40. The method of claim 26, wherein said at least one QoSparameter is used to estimate packet jitter to form a basis for saidhandoff trigger decision.
 41. The method of claim 26, further comprisingthe step of avoiding the gathering of said at least one QoS parametersby said collector packets for each router already visited by said firstand second probing packet from another access router.
 42. A method ofestimating QoS for making a handoff trigger decision for a remoteterminal in a wireless IP network, comprising the steps of: sending afirst and second probing packet across a fixed core network from aplurality of candidate access routers to a correspondent access router;sending a forward collector packet that follows said first and secondprobing packet across said fixed core network to said correspondentaccess router, wherein said forward collector packet collects apredetermined set of parameters from said routers; sending said firstand second probing packet and said forward collector packet back to saidoriginating access router from said correspondent access router; sendinga reverse collector packet that follows said first and second probingpacket across said fixed core network to said originating access routerfrom said correspondent access router, wherein said reverse collectorpacket collects a second predetermined set of parameters from saidrouters; and processing the first and second predetermined set ofparameters from said forward and reverse collector packets to make ahandoff trigger decision.
 43. The method of claim 42, further comprisingthe step of recording a packet queuing delay at each said router. 44.The method of claim 42, further comprising the step of recording apacket transmission time at each said router.
 45. The method of claim42, wherein said first and second predetermined set of parametersinclude a cumulated sum of queuing delays experienced by said first andsecond probing packets at each said respective router.
 46. The method ofclaim 42, wherein said first and second predetermined set of parametersinclude a transmission time of said first and second probing packetsfrom each said respective router.
 47. The method of claim 42, whereinsaid first and second predetermined set of parameters include acumulated sum of the current packet queuing delay at said routers. 48.The method of claim 42, wherein said first and second probing packetsare formed with the same characteristics as voice traffic packets. 49.The method of claim 42, wherein said first and second predetermined setof parameters are used to estimate one-way packet delay.
 50. The methodof claim 42, wherein said first and second predetermined set ofparameters are used to estimate available bandwidth.
 51. The method ofclaim 42, wherein said first and second predetermined set of parametersare used to estimate packet jitter.
 52. The method of claim 42, furthercomprising the step of avoiding the gathering of said firstpredetermined set of parameters for routers already visited by a firstand second probing packet from another access router.
 53. The method ofclaim 42, further comprising the step of avoiding the gathering of saidsecond predetermined set of parameters for routers already visited by afirst and second probing packet from another access router.